AP BIOLOGY

Detailed explanation-1: -Activation of receptors can trigger the synthesis of small molecules called second messengers, which initiate and coordinate intracellular signaling pathways. For example, cyclic AMP (cAMP) is a common second messenger involved in signal transduction cascades.

Detailed explanation-2: -The molecular components of these signal transduction pathways are always activated by a chemical signaling molecule. Signaling molecules can be grouped into three classes: cell-impermeant, cell-permeant, and cell-associated signaling molecules (Figure 8.3).

Detailed explanation-3: -Ligands that bind to RTKs include the fibroblast growth factors, epidermal growth factors, platelet-derived growth factors, and stem cell factor.

Detailed explanation-4: -Most molecules that lead to signal transduction are chemical substances, such as hormones, neurotransmitters, and growth factors, that bind to a specific protein receptor (signaling molecule) on or in a cell.

Detailed explanation-5: -As already noted, all signaling molecules act by binding to receptors expressed by their target cells. In many cases, these receptors are expressed on the target cell surface, but some receptors are intracellular proteins located in the cytosol or the nucleus.